1. Field of the Invention
The present invention relates to a magnetic head device.
2. Description of the Related Art
FIG. 6 is a plan view of a conventional hard disk device. The hard disk device comprises a magnetic disk 101, a spindle motor 102 which rotationally drives the magnetic disk 101, a carriage 103, a load beam 104, a slider 105, and a voice coil motor 106. A magnetic head device is roughly formed by the load beam 104 and the slider 105.
A base end portion 104b of the load beam 104, which is a resilient supporting member, is connected to an end portion 103a of the carriage 103, which is a rigid member. The slider 105 is mounted to an end 104a of the load beam 104 through a flexure (not shown).
The carriage 103 and the load beam 104 are driven in a radial direction of the magnetic disk 101 by the voice coil motor 106 in order to carry out a seek operation and a tracking operation. The seek operation is carried out to move a reproducing element and a recording element, which are mounted to the slider 105, above any recording track. The tracking operation is carried out to achieve fine adjustment so as to maintain the positions of the reproducing element and the recording element above a centerline of a recording track.
In order to increase recording density, it is necessary to increase the precision of the tracking operation by increasing the driving frequency of the voice coil motor 106. Since the driving frequency of the voice coil motor 106 is related to the resonant frequency of the load beam 104, there is a limit as to how high the driving frequency of the voice coil motor 106 can be made. Thus, there is a limit as to how high the precision of the tracking operation can be made.
To overcome this problem, a magnetic head device which has a microactuator mounted to the load beam 104 has been developed. The magnetic head device can carry out a tracking operation as a result of moving only an end portion of the load beam 104 by the microactuator.
FIG. 7 is a perspective view of the load beam 104. FIG. 8 is a sectional view of the main portion of FIG. 7.
The load beam 104 is formed of a stainless-steel plate spring material, and includes a stationary base end portion 111a and a swinging portion 111b. The stationary base end portion 111a is held by the carriage, and the swinging portion 111b can swing horizontally with respect to the stationary base end portion 111a. Arms 111c and 111c, which extend in the longitudinal direction of the stationary base end portion 111a, are formed on both sides of the front end portion of the stationary base end portion 111a. The swinging portion 111b is connected to the arms 111c and 111c through resilient supporting portions 111d and 111d. 
Piezoelectric elements 112 and 113, which are microactuators, are placed on the swinging portion 111b and the stationary base end portion 111a by placing them over a gap 111e. 
The piezoelectric element 112 comprises a piezoelectric layer 112a and electrode layers 112b and 112c. The piezoelectric element 113 comprises a piezoelectric layer 113a and electrode layers 113b and 113c. The piezoelectric layers 112a and 113a are formed of, for example, lead zirconate titanate (PZT). The electrode layers 112b and 112c and 113b and 113c are formed of, for example, metallic films deposited onto the top and bottom sides of their corresponding piezoelectric layers 112a and 113a. 
As shown in FIG. 8, the electrode layers 112c and 113c of the corresponding piezoelectric elements 112 and 113 and the swinging portion 111b and the stationary base end portion 111a are joined together by an electrically conductive adhesive resin 115.
In FIG. 7, reference numeral 121 denotes a slider which is mounted to an end of the swinging portion 111b through a flexure (not shown).
As shown in FIG. 8, the load beam 104 is connected to ground. As shown in FIG. 7, the electrode layer 112b of the piezoelectric element 112 and the electrode layer 113b of the piezoelectric element 112 are connected by a gold wire 114a. As shown in FIGS. 7 and 8, a different gold wire 114b is connected to the electrode layer 113b of the piezoelectric element 113, and to a control circuit 114c. By virtue of this structure, a control voltage can be applied to the piezoelectric elements 112 and 113 from the control circuit 114c. 
The piezoelectric elements 112 and 113 are elements which get distorted when a voltage is applied through the electrode layers 112b and 112c, and 113b and 113c, respectively.
The piezoelectric layers 112a and 113a of the corresponding piezoelectric elements 112 and 113 polarize in the film thickness directions. However, the polarization directions are opposite each other. Therefore, when the same control voltage is applied to the electrode layers 112c and 113c, one of the piezoelectric elements expands in the longitudinal direction thereof, while the other piezoelectric element contracts in the longitudinal direction thereof.
As a result, the resilient supporting portions 111d and 111d get distorted, so that the position of the slider 121, mounted to an end of the swinging portion 111b, changes. In other words, a precise tracking operation can be carried out by slightly moving the slider 121, mounted to an end of the swinging portion 111b, in the widthwise direction of a track.
As the recording density of the magnetic disk 101 increases, it becomes necessary to increase the precision of the tracking operation. By the load beam 104, it is possible to carry out a precise tracking operation, so that the recording density can be increased.
The electrically conductive adhesive resin 115 is required to maintain electrical conduction between the load beam 104 and the piezoelectric elements 112 and 113, and to function so that the deformation of the piezoelectric elements 112 and 113 reliably causes deformation of the load beam 104 by increasing the bonding strength between the load beam 104 and the piezoelectric elements 112 and 113.
However, the commonly used electrically conductive adhesive resin 115 is an epoxy adhesive resin mixed with, for example, a metal filler. Since the bonding strength is reduced by mixing the metal filler, the deformation of the piezoelectric elements 112 and 113 cannot reliably cause deformation of the load beam 104, thereby giving rise to the problem that a precise tracking operation cannot be carried out.
The electrically conductive adhesive resin 115 tends to deteriorate at a high temperature. Therefore, when, for example, the magnetic head device is continuously operated for a long period of time, the temperature of the whole magnetic head device rises, so that the bonding strength of the electrically conductive adhesive resin 115 is reduced, thereby also resulting in the problem that a precise tracking operation cannot be carried out.
In view of the above-described situation, it is an object of the present invention to provide a magnetic head device which can precisely carried out a tracking operation as a result of increasing bonding strength between a piezoelectric element and a load beam.
To this end, the present invention uses the following structures.
According to the present invention, there is provided a magnetic head device comprising a slider having provided thereat a reproducing element and a recording element, with the reproducing element being used to detect a magnetic signal recorded on a recording medium and a recording element being used to record a magnetic signal on the recording medium; a resilient supporting member which supports the slider; and a piezoelectric element, mounted on the resilient supporting member, for changing the position of the slider by distorting the resilient supporting member. In the magnetic head device, the piezoelectric element comprises a piezoelectric layer and a pair of electrode layers which sandwich the piezoelectric layer. The resilient supporting member comprises a stationary base end portion and a swinging portion, the swinging portion supporting the slider as a result of being connected to the stationary base end portion, and the swinging portion being swingable with respect to the stationary base end portion by the piezoelectric element. With one of the electrode layers of the piezoelectric element opposing the stationary base end portion and the swinging portion, the piezoelectric element is disposed so as to be placed on both the stationary base end portion and the swinging portion. A surface of the one of the electrode layers, the stationary base end portion, and the swinging portion are joined together through an electrically conductive adhesive resin, and both end portions of the piezoelectric element in directions in which the piezoelectric element expands and contracts, the stationary base end portion, and the swinging portion are joined together through a nonconductive adhesive resin.
According to the magnetic head device, the piezoelectric element is joined to the stationary base end portion and the swinging portion by an electrically conductive adhesive resin and a non-conductive adhesive resin. Therefore, compared to the case where only an electrically conductive adhesive resin is used, the bonding strength can be increased, so that the resilient supporting member is reliably deformed in correspondence with the deformation amount of the piezoelectric element. Therefore, it is possible to increase the precision of a tracking operation.
In addition, since a non-conductive adhesive resin is applied to both end portions of the piezoelectric element in the directions in which the piezoelectric element expands and contracts, the non-conductive adhesive resin does not interfere with the expansion and contraction of the piezoelectric element. Therefore, it is possible to increase the precision of the tracking operation.
Further, when the non-conductive adhesive resin is applied to both end portions of the piezoelectric element, even if the non-conductive adhesive resin is applied to both electrode layers which sandwich the piezoelectric layer, a short circuit does not occur between the electrode layers because the non-conductive adhesive resin is not electrically conductive.
In the magnetic head device, a lead used for applying a voltage may be connected to the other electrode layer of the piezoelectric element, and the nonconductive adhesive resin may be applied from both end portions of the piezoelectric element to part of the other electrode layer and to a connection portion of the lead and the other electrode layer.
According to the magnetic head device, by applying the non-conductive adhesive resin to both end surfaces of the piezoelectric element and part of the other electrode layer, and to the connection portion of the lead and the other electrode layer, the lead connection portion can be protected by the non-conductive adhesive resin, thereby making it possible to reinforce the bonding strength between the lead connection portion and the other electrode layer. Therefore, it is possible to prevent breakage of the lead from the second electrode layer.
The non-conductive adhesive resin is applied to both electrode layers which sandwich the piezoelectric layer. Since the non-conductive adhesive resin is not electrically conductive, a short circuit between the electrode layers does not occur.